Autofrettage process and autofrettage apparatus

Abstract

In the autofrettage process, a thick-walled workpiece ( 2 ) to undergo autofrettage is positioned in an autofrettage apparatus ( 1 ). The interior space ( 5 ) of the workpiece ( 2 ) is filled with a fluid and closed so as to be pressure-tight. The volume available to the fluid in the interior space ( 5 ) of the workpiece ( 2 ) is reduced by a displacement piston ( 19 ) which is moved into the interior space ( 5 ) of the workpiece ( 2 ) through a displacement piston opening ( 6 ) of the workpiece ( 2 ). The pressure is therefore generated in the interior space ( 5 ) of the workpiece ( 2 ).

What is claimed is: 
     
       1. An autofrettage process, wherein interior regions of a workpiece are permanently plastically deformed under high pressure, whereas exterior regions of the workpiece are only elastically deformed, the process comprising the steps of:
 placing a workpiece having an interior space and a displacement piston opening in an autofrettage apparatus, 
 filling the interior space of the workpiece from below with a fluid through a pre-fill opening, 
 closing the pre-fill opening with a closure piston, 
 venting air from a region of the displacement piston opening, until the fluid flows out of the displacement piston opening of the workpiece disposed at a top of the workpiece, 
 sealing the interior space of the workpiece by pressing a sealing sleeve surrounding the closure piston against a flange face of the workpiece so as to be pressure-tight, and 
 advancing a displacement piston through the displacement piston opening into the interior space of the workpiece to reduce a volume available to the fluid in the interior space. 
 
     
     
       2. The autofrettage process of  claim 1 , wherein the displacement piston opening is sealed by a sealing cone which is pressed against an edge of the displacement piston opening. 
     
     
       3. The autofrettage process of  claim 1 , wherein the sealing sleeve is pressed against the flange face by the closure piston using a spring. 
     
     
       4. The autofrettage process of  claim 3 , wherein a periphery of the closure piston is sealed against the sealing sleeve by a sealing ring, wherein the sealing sleeve is carried along by the closure piston through friction from the sealing ring. 
     
     
       5. The autofrettage process of  claim 1 , wherein the displacement piston opening and the pre-fill opening are located opposite one another, wherein a force closing the opposing openings increases proportional to an autofrettage pressure applied by advancing the displacement piston. 
     
     
       6. The autofrettage process of  claim 1 , further comprising the steps of:
 retracting the displacement piston from the workpiece, after reaching an autofrettage pressure, until a pressure in the interior space is approximately identical to ambient pressure, 
 lifting the sealing cone from the displacement piston opening, 
 lifting the closure piston from the pre-fill opening, and 
 lifting the sealing sleeve from the flange face, and 
 removing the workpiece that underwent autofrettage from the apparatus. 
 
     
     
       7. The autofrettage process of  claim 1 , wherein the workpiece is a component that carries fuel.